Apparatuses and methods for pre-erasing during manufacture of magnetic tape

ABSTRACT

The present invention relates to direct current (“DC”) pre-erasing servo channels of a magnetic tape prior to writing servo data in a servo channel. The present invention particularly relates to those servo recordings which were written with a uni-polar current waveform. The DC pre-erase is performed using a uni-polar direct current of a polarity that is opposite to the polarity of the direct current used to write the servo data. This pre-erase may be done with one or more heads. Also, as will be described, the pre-erase of a servo channel and writing to a servo channel may be done by making two passes over a single head or by using two or more heads to perform both steps. Also, it is within the scope of the present invention to have the heads mounted on a single mount or have the heads on separate mounts and on separate tape decks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/838,006, filed on Aug. 13, 2007, which is a continuation of U.S.patent application Ser. No. 10/768,719, filed on Jan. 30, 2004, issuedas U.S. Pat. No. 7,283,317, the contents of each of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to apparatuses and methods for use in themanufacture of magnetic tape. In particular, the present inventionrelates to apparatuses and methods for pre-erasing a servo channel of amagnetic tape.

BACKGROUND OF THE INVENTION

Magnetic tape as a data storage medium requires the ability toeffectively write and read data to data tracks of the magnetic tape;many such data tracks typically extend linearly along the length of tapeand, in part, define tape data storage density. In addition, forproviding a controlled movement of tape reading and/or writing headswith respect to the data track, servo tracks, which also extend linearlyalong the length of tape are commonly used. Servo tracks are typicallywritten in such a way as to span the tape in an efficient manner thatmaximizes the number of data tracks and minimizes the number of servotracks for a given tape system.

A servo track contains servo data and is read by a servo read head. Thisinformation is used to determine the relative position of the servo readhead with respect to the magnetic media in a translating direction(i.e., movement across the width of the tape). This is also called thecross track direction. To improve positioning of the tape reading and/orwriting heads on a magnetic tape, apparatuses and methods of manufactureto create a servo channel that enables the servo data to be read moreeffectively would be helpful. The present invention addressesapparatuses and methods to improve a servo control system.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to direct current (“DC”) pre-erasing servochannels of a magnetic tape prior to writing servo data in a servochannel. The present invention particularly relates to those servorecordings which were written with a uni-polar current waveform. The DCpre-erase is performed using a uni-polar direct current of a polaritythat is opposite to the polarity of the direct current used to write theservo data. This pre-erase may be done with one or more heads. Also, aswill be described, the pre-erase of a servo channel and writing to aservo channel may be done by making two passes over a single head or byusing two or more heads to perform both steps. Also, it is within thescope of the present invention to have the heads mounted on a singlemount or have the heads on separate mounts and on separate tape decks.

In one embodiment, the present invention relates to a magnetic tapecomprising a substrate and a magnetic layer, the magnetic tape having atleast one direct current pre-erased servo channel that includes servodata.

In another embodiment, the present invention relates to a magnetic tapehaving at least one servo channel that is direct current pre-erased andhas servo data written in the at least one servo channel.

The magnetic tape is made by a method comprising writing a servo patternusing a uni-polar direct current of a particular pulse train. Prior towriting a servo pattern, erasing the servo channel of the magnetic tapeby applying a direct current of a substantially opposite polarity tothat of the servo write current pulse sequence.

The present invention also relates to an apparatus for use inpre-erasing magnetic tape, comprising a housing supporting at least twoheads, wherein at least one of the two heads includes a gap pattern todirect current pre-erase the servo channels on the magnetic tape,wherein the other of the two heads includes a gap pattern for recordingthe servo channel that is written after the pre-erase has been firstrecorded.

The present invention further relates to an apparatus for use inpre-erasing magnetic tape, comprising a compound substrate having atleast a first substrate and a second substrate, wherein the firstsubstrate includes at least one servo pattern and the second substrateincludes at least one direct current pre-erase pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a typical servo track and data track organization on thetape.

FIG. 2 is a schematic drawing of one embodiment of the present inventionshowing a housing supporting two heads with magnetic tape extending overthe heads, where one of the heads is used to pre-erase with directcurrent the servo channels of a magnetic tape and the other is used torecord the servo pattern onto the pre-erase servo channels.

FIG. 3 is a schematic drawing of one embodiment of the present inventionshowing a housing supporting one head with the magnetic tape extendingover the head, where the head is used to pre-erase with direct currentthe servo channels of a magnetic tape.

FIG. 4 shows an exemplary servo erase gap pattern on the surface of asurface film head.

FIG. 5 shows an exemplary servo gap pattern on the surface of a surfacefilm head that may be used to write a servo pattern in the servo channelon a magnetic tape.

FIG. 6 shows a two head configuration in which one head has a gappattern that would be used to DC pre-erase the servo channel and theother head has a timing based servo gap pattern that would write atiming based pattern onto the servo channel on a magnetic tape.

FIG. 7 shows a close-up of the patterns shown in FIG. 6. Note that thepatterns are matched so that the erase track width is substantially thesame as the servo track width.

FIGS. 8A-8B show a portion of a magnetic layer and substrate of amagnetic tape and a theoretical output signal from a servo pattern on amagnetic tape in which the tape and servo channel have been AC erased.

FIGS. 8C-8D show a portion of a magnetic layer and substrate of amagnetic tape and a theoretical output signal from a servo pattern on amagnetic tape in which the servo channel has been DC erased prior torecording the servo signal.

FIGS. 9A and 9B show theoretical waveforms for relating themagnetoresistive (MR) response curve of the head, an input field fromthe magnetic tape, and an output voltage signal from the MR headelement.

FIG. 10 shows a two head configuration in which one head is a ferriteMIG head having a gap pattern that would be used to DC pre-erase theservo channel and the other head is a surface thin film head using thelow inductance, ferrite sub-gap substrate having a timing based servogap pattern that would write a timing based pattern onto the servochannel on a magnetic tape.

FIG. 11 shows an embodiment of the present invention using a compoundsubstrate.

FIG. 12 is a schematic drawing of one embodiment of the presentinvention showing a first housing supporting one head with the magnetictape extending over the head, where the head is used to pre-erase withdirect current the servo channels of a magnetic tape and a secondhousing supporting one head with magnetic tape extending over the head,where the head is used to write servo data in the servo channel of themagnetic tape.

DETAILED DESCRIPTION

The present invention relates to apparatuses and methods used inmanufacturing magnetic tape. In particular, the present inventionrelates to manufacture of magnetic tape that includes servo data in oneor more servo channels, where one or more servo channels has beenpre-erased with a uni-polar signal prior to the servo data being writtenin a servo channel. Pre-erasing a servo channel with direct currentenables the servo read signal representing the uni-polar written servopattern to be stronger than a servo read signal in a similar servochannel that is not pre-erased. As such, pre-erasing the servo channelduring the manufacture and formatting of the magnetic tape will providebenefits by increasing the signal to noise ration of the servo readsignal. This in turn can lead to higher areal data storage densities forthe magnetic tape. However, it is important to note that the response ofa magnetoresistive (“MR”) head to this technique may be too strong andresult in distortion and non-linear servo read signals. Hence thistechnique is to be used when the media thickness and M.sub.rt ratio hasbecome smaller in more aggressive higher density products and when usingsuch a technique will not overdrive the MR servo read head. Since theresult of this technique is to increase the servo read signal, it isimportant to not use it if it will send the read head into a non-linearresponse region. On the other hand, as areal densities are everincreasing and typically accompanying this the M.sub.rt ratio isdecreasing, the use of this technique may prove beneficial in certainservo systems as tape thicknesses continue to decrease.

FIG. 1 shows a magnetic tape 10 having data bands or data tracks 12(also, may be referred to as data channels) and servo bands or servotracks 14 (also may be referred to servo channels). The data tracks 12would be the portion of tape 10 to which data elements 16 would bewritten and from which data elements 16 would be read. Similarly, servotracks 14 would include servo data 18 which are written into the servotrack during manufacture of the magnetic tape 10. This servo data 18 isused by the servo control system to help properly position the read andwrite heads with respect to the data tracks 12. The present inventionrelates to pre-erasing servo tracks 14 with a direct current oruni-polar pre-erase signal prior to writing a uni-polar servo pattern ofthe opposite polarity in the servo track 14.

In the preferred embodiment, only the servo channels 14 of a magnetictape 10 are pre-erased by applying a uni-polar, direct current erasesignal through a precise gap pattern in the head. A uni-polar servopattern is then written upon the pre-erased servo channel but in theopposite polarity. The servo pattern may be timing based or amplitudebased or a combination of both. However, the present invention willtypically be used with a time based pattern as timing patterns aretypically uni-polar and amplitude patterns are typically bi-polar. Onbi-polar current written or recorded servo channels 14, the technique isless effective in increasing the signal-to-noise (“SNR”) of the servoread system.

In manufacturing magnetic tape 10, the DC pre-erase and the writing of aservo pattern may be accomplished using two or more heads or using onehead. For instance, in one embodiment, a portion of the magnetic tape 10is first passed over a head to perform a DC erase of servo channels 14of the magnetic tape 10 and then another head is used to write a servopattern into the servo channels 14 of the magnetic tape 10.Alternatively, the same head may be used to perform a DC erase of theservo channels 14 on a magnetic tape 10 and then to write a servopattern in the servo channels 14 of the magnetic tape 10. That is, inthis embodiment, the magnetic tape 10 is passed over the head to performa DC erase of the servo channels 14. A pulse is applied through thepattern in the head to DC erase the servo channels 14 of the magnetictape 10. Then, the tape 10 is passed over the head a second time towrite a servo pattern into the servo channels 14 of the magnetic tape10.

In one embodiment, two heads are used and are mounted into a housing sothat an efficient one pass servo formatting system may be used. Thisembodiment is shown in FIG. 2. However, each head may be separatelysupported by a separate housing or even a separate tape deck (as shownin FIG. 12).

With reference to FIGS. 2 and 3, embodiments of an apparatus for use inDC pre-erasing a servo channel 14 of a magnetic tape 10 will bedescribed. FIG. 2 shows a housing 20 with magnetic tape 10 extendingacross the two heads 22, 22′. As shown in FIG. 2, the embodimentincludes a housing 20 that supports a first head 22 and a second head22′. The heads have a first surface 24, 24′, a second surface 26, 26′, afirst side surface 28, 28′, and a second side surface 30, 30′. The firstsurface 24, 24′ is in contact with the magnetic tape 10. The secondsurface 26, 26′ of the heads is attached to and supported by the housing20. In one embodiment, the heads 22, 22′ are mounted to the housing anepoxy. However, the heads may be mounted using any suitable means.

The heads 22 and 22′ are disposed side-by-side separated by apredetermined distance L. As shown in FIG. 2, in one embodiment, theheads 22 and 22′ are spaced apart approximately 1.0 millimeters (“mm”)around the top edge 29, 29′ (i.e., toward the first surface 24) andspaced apart approximately 0.80 mm at the bottom edge 31, 31′ (i.e.,toward the second surface 26). It will be appreciated that while thedistance between the heads is specified, other distances may be used.Similarly, the angle A formed between the two heads may be varied andeven flat contours may be used. While FIG. 2 shows the heads 22 and 22′not spaced such that the sides 30, 28′ are parallel to each other, theheads may be spaced in such a manner that the sides 30, 28′ of the firstand second heads 22 and 22′ are substantially parallel to each other inthe vertical direction as shown.

Any type of head may be used in the dual head configuration including,but not limited to thin film heads, ferrite based heads, and surfacethin film heads. For instance, the first and second heads 22 and 22′ maybe heads with low inductance, ferrite sub-gap substrate surface filmhead structures of the type described in U.S. Pat. No. 6,496,328, whichis hereby incorporated by reference in its entirety, a surface thin-filmhead of the type disclosed in U.S. Pat. No. 6,269,533, which is herebyincorporated by reference in its entirety, or a ferrite metal-in-gap(“MIG”) head. Any combination of these types of heads may be used whenusing two or more head in implementing an embodiment of the presentinvention. It will be noted that one head will be optimized as an erasehead and the other head will be optimized as a servo write head.

In one embodiment of the dual configuration (as shown in FIG. 10), aferrite MIG head or a surface thin film head with a pattern would beused to perform the DC erase and a surface thin film head using the lowinductance, ferrite sub-gap substrate surface film head with a time baseservo pattern would be used to write a servo pattern on the servochannel of the magnetic tape. FIG. 10 shows a ferrite MIG head with apre-erase gap 46 to perform a DC erase with a surface thin film headhaving gap for an amplitude or a time based servo pattern for writing toa servo channel 14. As shown in FIG. 10, the width of the pre-erase gapis substantially the same as the width of the servo pattern.

The housing 20 may be formed from any appropriate material includingmetal. The housing 20 is milled to position the heads 22, 22′ to thehousing. Furthermore, it will be appreciated that while FIG. 2 shows ahousing that includes two heads, a housing having more than two heads iswithin the scope of the present invention.

FIG. 3 shows a housing mount 20 that has a first head 22. Thisembodiment may be used when the heads for performing the DC pre-erase onthe servo channels 14 and writing the servo patterns on the servochannels 14 are located on different tape decks or this embodiment maybe used when the same head is used to perform both the DC erase on onepass and write the servo data 18 on the servo track 14 on a second pass.FIG. 12 shows a first housing 20 supporting a first head 22 with themagnetic tape 10 extending over the head 22, where the head is used topre-erase with direct current the servo channels 14 of a magnetic tape10 and a second housing 20′ supporting a second head 22′ with magnetictape 10 extending over the second head 22′, where the second head 22′ isused to write servo data in the servo channel 14 of the magnetic tape10.

FIG. 11 shows an alternative embodiment that may be used for moreprecise pattern combinations than a mechanically assembled dual modulehead pair. FIG. 11 shows a compound substrate 80. As shown in FIG. 11,the compound substrate 80 has a first substrate 81 and a secondsubstrate 83. The first and second substrates 81 and 83 are spaced aparta predetermined distance L by use of a first block 85 to separate thesubstrates. The first substrate includes a pre-erase gap 46 to DC erasea servo channel and the second substrate includes a servo pattern thatis written in the DC pre-erased servo channel. As shown in FIG. 11, thepre-erase gap is ideally substantially the same width at the servopattern. The pre-erase gap may have a slightly larger width than thewidth of the servo pattern. The first block 85 separating the compoundsubstrate may be formed with ceramic. However, other materials may beused to separate the substrates. The substrates may be joined togetherusing epoxy.

FIG. 11 shows a compound substrate 80 having a combination of a surfacethin film head (of the type described in U.S. Pat. No. 6,269,533) and alow inductance surface thin film head (of the type described in U.S.Pat. No. 6,496,328). Also, while two substrates are joined together inFIG. 11, a compound substrate having more than two substrates is withinthe scope of the present invention.

The compound substrate in FIG. 11 may have all the gaps lithographicallyprinted by a single mask and hence all patterns printed on thosesub-gaps will have lithographic precision to the order of 0.1 microns orbetter. Hence, the compound substrate module may be used for moreprecise pattern combinations than a mechanically assembled dual modulehead pair.

The apparatuses discussed with respect to FIGS. 2 and 3 may containvarious servo patterns where one of the patterns is for performing a DCpre-erase of a servo track 14. FIG. 4 shows an exemplary servo erase gappattern on the surface of a surface film head. While the servo headitself of FIG. 5 may be used to pre-erase the tape 10 this would requirea two pass operation which would be time inefficient. However that wouldbe within the scope of the present invention.

FIG. 4 shows an exemplary servo erase gap pattern on the surface of asurface film head. The servo erase gap pattern 32 includes a firsttermination 34 and a second termination 36. The terminations 34, 36 mayhave curved portions. As shown in FIG. 4, the terminations 34 and 36 arecircular. FIG. 5 shows an exemplary servo gap pattern on the surface ofa surface film head that may be used to write a servo pattern in theservo channel 14 on a magnetic tape 10. FIG. 5 shows a servo gap pattern38 that is time based. The servo gap pattern 38 has a first portion 40and a second portion 40′, with each portion 40, 40′ having a firsttermination 42, 42′ and a second termination 44, 44′. As with thepattern in FIG. 4, the terminations 42, 42′, 44, 44′ have curvedportions, and as shown, have circular terminations. It will beappreciated that other types servo patterns may be used withoutdeparting from the scope of the present invention.

FIG. 6 shows a two head configuration in which one head has a gappattern 32 that would be used to DC pre-erase the servo channel and theother head has a timing based servo gap pattern 38 that would write atiming based pattern onto the servo channel on a magnetic tape 10. FIG.7 shows a close-up of the patterns shown in FIG. 6. Note that thepatterns are matched so that the erase gap track width is substantiallythe same as the servo gap track width. Such a configuration would allowthe entire servo track 14 to be DC erased

FIGS. 4-6 show each head having five patterns that may be used toperform a DC pre-erase. Such heads may have the same number of patternsto perform a pre-erase as the number of servo channels or servo tracks14 contained on the magnetic tape 10.

A pre-erase process may be performed during the production of magnetictape in order to provide a stronger signal for reading the servopattern. FIG. 8A shows magnetic tape 10 with servo track 14, wherein theservo track 14 has been AC erased but not DC erased. As shown in FIG.8A, the magnetic tape 10 has a magnetic layer 11 and a substrate 13. The“M” stands for magnetization and shows that a portion 19 of the servochannel 14 is magnetized (e.g., by the writing of servo data). FIG. 8Bshows the input signal 50 from a tape 10 as read by a read head of theservo pattern 14 in such a condition. The amplitude B indicates, atleast in part, the strength of the signal 50.

FIG. 8C shows magnetic tape 10 with servo track 14, wherein the servotrack has been DC erased in accordance with the present invention. As inFIG. 8A, the servo channel 14 has be magnetized by the written servodata. However, unlike FIG. 8A, the portion of the servo channel adjacentthe servo data has been DC pre-erased. FIG. 8D shows the input signal 52from the tape 10 as read by the servo read head in such a condition. Theamplitude C indicates the strength of the input signal 52 from the DCpre-erased servo channel is theoretically greater than the input signal50 from the servo channel that was not DC pre-erased. A comparison ofFIGS. 8B and 8D shows that, in theory, the input signal 52 from a DCpre-erased servo channel is greater than the input signal 50 from aservo channel that has not been DC pre-erased. In one embodiment, a DCpre-erased channel, in theory, would provide a servo read voltage signaltwice as strong as an input signal from a servo channel that has notbeen DC pre-erased but which had been randomly erased.

FIGS. 9A and 9B show a theoretical response curve 70 of the MR stripe, atheoretical input signal from a tape 71 and a theoretical output voltage72. The response curve 70 includes a peak 73 and a portion thatapproximates a linear region 74. This response curve is sometimereferred to the cosine squared response as the curve can be modeled as.DELTA.R=(.delta..rho./.rho.)R cos.sup.2.phi.). The angel .phi. beingthe angle between the resultant magnetization vector of the MR stripeand the applied current direction in the stripe. (.delta..rho./.rho.) iscalled the magnetoresistive coefficient of the material that makes upthe stripe.

This response curve in turn leads to a voltage .DELTA.V=I.DELTA.R, whereI is the bias current of the stripe. This discussion could equally applyto giant magnetoresistive (“GMR”) materials where the response issimilar but modeled as a cosine curve.

In general, the output voltage should correspond to a waveform shown inFIG. 9A in which the input signal is within the linear region of theresponse curve. However, as shown in FIG. 9B, when the output voltagehas a “rabbit ears” 75, that the input signal extends outside the linearregion and, as shown, to the negative slope of there response curve.

This condition is not desired. As such, the DC pre-erase must be suchthat the signal output remains within the liner region of the responsecurve. As such, the present invention when used appropriately allows forgreater voltages of the input signal while still remaining in the linearregion of the response curve.

Also, in general, the MR read sensor output voltage is a function of thethickness of the magnetic tape. To achieve higher linear recordingdensities the tape thickness is generally decreased to maintain magneticbit cell stability. Hence the servo read signals may need to beincreased as tape thickness decreases. As such, under proper conditions,and assuming certain system parameters of higher density recordings,performing a DC pre-erase of a servo channel enables a stronger signalto be read without going into the non-linear region of the MR readelements response curve.

In practical operation, a dual head system consisting of a servo writehead and servo DC erase head would be used in making magnetic tape. Theservo DC erase will erase only that part of the medium upon which willbe recorded the servo format signal. For all practical purposes, the DCerase head track widths and the servo format head track widths would bethe same and they would be matched up within certain engineeringtolerances. That is, the magnetic tape would only be DC erased in theservo track region and not in the data track regions. This is becausedata zones should remain ideally AC erased so that the subsequent datawritten thereupon will have the highest possible signal-to-noise rationand the data will not be biased by the underlying DC erasure.

In principle one could wipe the entire tape width with a DC erase andachieve the same result on the servo track, however that may compromisethe subsequently recorded data in the data track areas. Hence, while onecould use a full tape width DC erase head this would not be preferredmethod for reasons that go beyond the scope of this document.

During manufacture, the magnetic tape would move in a transducingdirection over the heads. The servo channel of the magnetic tape isfirst pre-erased, and then a servo pattern is written in the servochannel 14 (see FIG. 1). The resulting magnetic tape 10 would have apre-aligned magnetization of the opposite polarity to that of the servosignal.

The dual module head system on one mount, the dual heads on separateindividual mountsor the compound substrate head may be used to enablethis concept. This concept can apply to timing based servo systems,amplitude based systems or a combination of both in some more advancedservo system. The concept will be most effective when the servo writesystem is uni-polar in nature and when the DC pre-erase is made usingthe opposite polarity.

In that the foregoing description of the present invention disclosesonly exemplary embodiments thereof, it is to be understood that othervariations are contemplated as being within the scope of the presentinvention. Accordingly, the present invention is not limited in theparticular embodiments which have been described in detail therein.Rather, reference should be made to the appended claims as indicative ofthe scope and content of the present invention.

1. A method for making a magnetic media, the method comprising:pre-erasing at least one servo channel of the magnetic media, withoutdirect current pre-erasing the data channels of the magnetic media, byapplying a direct current of a first polarity; and writing a servopattern by applying a direct current of substantially opposite polarityof the first polarity.
 2. The method of claim 1, wherein the pre-erasingand the writing is performed using a compound magnetic recording head.3. The method of claim 2, wherein the compound magnetic recording headcomprises: a first head comprising a magnetically permeable thin filmlayer comprising an erase gap pattern for pre-erasing a servo track of amagnetic media; and a second head comprising a magnetically permeablethin film layer comprising a servo write gap pattern for writing a servopattern in the servo track.
 4. The method of claim 3, wherein the erasegap pattern of the first head and the servo write gap pattern of thesecond head are lithographically printed using a single mask.
 5. Themethod of claim 4, wherein pre-erasing at least one servo channel isperformed by passing a portion of the magnetic media over the erase gappattern of the first head and writing a servo pattern is performed bythen passing a portion of the magnetic media over the servo write gappattern of the second head.
 6. The method of claim 5, wherein the servowrite gap pattern of the second head is a timing-based servo pattern. 7.The method of claim 5, wherein the servo write gap pattern of the secondhead is an amplitude-based servo pattern.
 8. The method of claim 1,wherein prior to pre-erasing at least one servo channel of the magneticmedia, the magnetic media is alternating current erased.
 9. A magnetictape having at least one servo channel that is direct current pre-erasedand has servo data written in the at least one servo channel and atleast one alternating current pre-erased data channel for receiving datasubsequently written thereon, the magnetic tape made by a methodcomprising: writing a servo pattern using a direct current of a firstpolarity; prior to the act of writing a servo pattern, erasing at leastone servo channel of the magnetic tape by applying a direct current of asubstantially opposite polarity of the first polarity.
 10. The magnetictape of claim 9, wherein the act of writing and erasing is performedusing a first head.
 11. The magnetic tape of claim 10, wherein the firsthead comprises a time-based servo pattern.
 12. The magnetic tape ofclaim 10, wherein the first head comprises an amplitude-based servopattern.
 13. The magnetic tape of claim 10, wherein the act of erasingat least one servo channel of the magnetic tape is performed by firstpassing a portion of the magnetic tape that includes the at least oneservo channel to be erased over the first head.
 14. The magnetic tape ofclaim 13, wherein the act of writing a servo pattern in the at least oneservo channel of the magnetic tape is performed by then passing aportion of the magnetic tape that includes the at least one servochannel to be written over the first head.
 15. The magnetic tape ofclaim 9, wherein the act of erasing is performed by a first head and theact of writing a servo pattern is performed by a second head.
 16. Themagnetic tape of claim 15, wherein the second head includes a time basedservo pattern.
 17. The magnetic tape of claim 15, wherein the secondhead includes an amplitude-based servo pattern.
 18. The magnetic tape ofclaim 15, wherein the first head includes an erase pattern having anerase gap track width that is substantially the same as the servo gaptrack width.
 19. The magnetic tape of claim 15, wherein the second headis one of a thin film head, ferrite based head, and surface thin filmhead.
 20. The magnetic tape of claim 15, wherein the two heads arelocated on a single mount.
 21. The magnetic tape of claim 15, whereinthe two heads are located on separate mounts.
 22. The magnetic tape ofclaim 15, wherein the head used to erase is located on a separate tapedeck from the head used to write a servo pattern.